One example of an electronic device that can perform data processing and memory access functions is a touch surface device typically used as an input device for performing operations in a computer system. Such input devices generate output signals based on user touches of a touch-sensitive surface or panel of the device. The operations generally correspond to moving a cursor and/or making selections on a display screen. Touch pads and touch screens (collectively “touch surfaces”) are becoming increasingly popular because of their ease and versatility of operation as well as to their declining price. Touch surfaces allow a user to make selections and move a cursor by simply touching the surface, which may be a pad or the display screen, with a finger, stylus, or the like. In general, the touch surface recognizes the touch and position of the touch and the computer system interprets the touch and thereafter performs an action based on the touch.
Touch pads are well-known and ubiquitous today in laptop computers, for example, as a means for moving a cursor on a display screen. Such touch pads typically include a touch-sensitive opaque panel which senses when an object (e.g., finger) is touching portions of the panel surface. Touch screens are also well known in the art. Various types of touch screens are described in applicant's co-pending patent application Ser. No. 10/840,862, entitled “Multipoint Touchscreen,” filed May 6, 2004, which is hereby incorporated by reference in its entirety. As noted therein, touch screens typically include a touch panel, a controller and a software driver. The touch panel is generally a clear panel with a touch sensitive surface. The touch panel is positioned in front of a display screen so that the touch sensitive surface covers the viewable area of the display screen. The touch panel registers touch events and sends these signals to the controller. The controller processes these signals and sends the data to the computer system. The software driver translates the touch events into computer events. There are several types of touch screen technologies including resistive, capacitive, infrared, surface acoustic wave, electromagnetic, near field imaging, etc. Each of these devices has advantages and disadvantages that are taken into account when designing or configuring a touch screen.
Conventional touch surface devices typically include: driver circuitry for providing drive or stimulation signals to one or more electrodes on a touch panel; output sensing circuitry for receiving and processing output signals from the touch panel; and a controller for controlling the driver circuitry and receiving the processed output signals from the output sensing circuitry for performing further processing and performing one or more functions based on the processed output signals. Each of these circuits can include a plurality of devices or modules for performing specific functions. Some or all of these modules may be integrated into one or more integrated circuit chips, e.g., an application specific integrated circuit (ASIC). A more detailed discussion of these circuits can be found, for example, in co-pending and commonly owned application Ser. No. 11/649,998, entitled “Proximity and Multi-Touch Sensor Detection and Demodulation,” the entirety of which is incorporated by reference herein, and application Ser. No. 11/650,201, entitled “Channel Scan Logic,” the entirety of which is incorporated by reference herein.
The controller typically includes an embedded processor or controller, such as an ARM968 microprocessor, for example, associated peripheral devices (e.g., RAM, ROM, state registers), a data bus, associated interfaces that allow communications between one or more of the devices over the data bus, and at least one input/output (I/O) interface (e.g., a serial peripheral interface) for communicating with external devices, such as a host processor. The embedded processor executes various control and processing functions required by the touch surface device and can communicate with external devices via the I/O interface.
It has been found, however, that an embedded processor can be inefficient in performing certain functions, such as interpreting data and/or command packets and accessing internal and/or external memories, due to the fact that such actions typically require multiple instructions, steps and clock cycles for a processor to perform. Additionally, an embedded processor consumes relatively large amounts of power when performing these operations. Another disadvantage is that if for some reason the embedded processor is not functioning properly, internal memory access may be completely disabled.